Fluorinated ion exchange polymers having as the functional groups sulfonic acid groups or a salt thereof are now well known in the art. They find numerous uses, e.g., as the membrane in electrochemical cells such as fuel cells and electrolytic cells such as chloralkali cells; as the catalyst for many chemical reactions; and in other varied permselective processes such as reverse osmosis and ultrafiltration.
Ordinarily these polymers are fabricated into the desired product by melt processing while the polymer is still in the form of a melt-fabricable precursor wherein the functional groups are --SO.sub.2 X where X is F or Cl, preferably --SO.sub.2 F, and then the --SO.sub.2 X groups are converted to ion exchange form. There are, however, many times when it is desirable to use a liquid composition containing a polymer for fabricating a product to be prepared.
There are known in the art some solutions of some of the fluorinated polymers with sulfonyl groups. For example, solutions of such polymers having the functional groups still in the --SO.sub.2 F form in the perhalogenated liquid or in a perhalogenated liquid which contains a sulfonyl fluoride or a carboxylic ester group, as disclosed in U.S. application Ser. No. 176,595 filed Aug. 8, 1980, now U.S. Pat. No. 4,348,310. However, most such solvents are expensive and uncommon, and many are difficult to make.
Also known in the art are solutions of fluorinated polymers having low equivalent weight and the functional groups in the form of sulfonic acid, sulfonamide or sulfonate groups, in any organic solvent which will form a solution in water containing at least 5% by weight of the organic solvent, as disclosed in British Patent Specification 1,286,859. However, the solutions prepared therein are all of polymers having an equivalent weight below 1000, and the specific disclosure therein of polymers having at least 14 mole % of the repeating unit containing the functional group corresponds to an equivalent weight no greater than 1060. Such solutions of higher equivalent weight polymers of this kind cannot be made.
It would be of advantage to have available liquid compositions of higher equivalent weight fluorinated polymers having sulfonic acid or sulfonate groups. It is desirable to have the functional groups as sulfonic acid or sulfonate groups so that --SO.sub.2 X groups do not have to be hydrolyzed after fabrication of the article to be prepared. It is often desirable to have the higher equivalent weight polymers inasmuch as they swell less than the lower equivalent weight polymers when in contact with aqueous media.
It is therefore a principal object of this invention to provide a process for making a liquid composition which contains therein a fluorinated polymer of higher equivalent weight having sulfonic acid or sulfonate groups, and the liquid composition made by this process.
Another object is to provide a liquid composition of the higher equivalent weight sulfonate polymers useful for coating various substrates, casting film, and repairing defective membranes of similar polymers.
Other objects will become apparent hereinbelow.